Can Lionfish Be Kept With Seahorses? Full Compatibility Guide.

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Choosing suitable tankmates for seahorses can be daunting since these fish are so fragile and sedentary. However, under the right conditions, they can be paired with various fish. One potential tankmate we will discuss is lionfish and whether these fish are compatible with seahorses.

Lionfish is a type of predatory fish that cannot be kept with seahorses. These fish are voracious feeders and seahorses are due to fall prey. They are also very dangerous and can easily harm seahorses causing any sort of encounter to be potentially fatal. These two types of marine life should never share the same aquarium, the risks outweigh the potential of co-existence.

Lionfish may not be aggressive but their predatory nature is far too intense for vulnerable fish such as seahorses.

Normally seahorses require a species-specific aquarium in which they do best, however, due to the arrival of captive-bred seahorses they have become more hardy making it possible for them to be kept with other fish.

These possible tankmates must be suitable with similar natures and overall dispositions if not they can cause more harm than their worth.

Lionfish don’t meet the criteria of becoming suitable tankmates for seahorses, they are too ferocious in their eating, too predatory and they are extremely dangerous.

Finding the right type of tankmate for a lionfish is very difficult since they are skilled predators always on the scout for potential prey.

There is about a handful of possible tankmates that are compatible with lionfish, seahorses arent one.

Seahorses should never be kept with this deadly creature not even the dwarf species are compatible due to the high risks that are associated with this species of fish.

Why Are Lionfish And Seahorses Incompatible?

Predatory Nature.

Lionfish are carnivore predators that will prey on anything that can fit in their mouths. This leaves small fish susceptible to becoming prey.

Their ideal targets are small, slow-moving fish that they can easily trap with their suction-creating jaws. 

Seahorses can easily fall prey due to their small size and defenseless nature.

Rather than becoming tankmates with lionfish, seahorses will become their targets which they can consume without any hassle.


Lionfish are very dangerous as they have many different protective mechanisms working together to not only protect them from possible threats but to lure potential prey.

They are highly venomous, with dangerous stinging ability, and can swallow small prey with their predatory strategy.

They are not the fastest but they surely are efficient in imitating how slow and steady wins the race.

All these characteristics are the complete opposite of what makes a good seahorse tankmate. Deeming lionfish as an incompatible and deadly tankmate.

Messy Feeders

Lionfish are also messy feeders leaving traces of leftover food lingering in the water. When kept in a closed system this leftover food can break down releasing ammonia and other harmful chemicals.

Seahorses are also very messy eats and if they are paired with lionfish the bioload of that system will be too great for the filtration system.

Even with the use of the best filtration, it will put a strain on the system leading to a decline in water quality.

Seahorses require very strict water parameters and any significant imbalances can leave them compromised to the point of death.

This is just another way that highlights the incompatibility of lionfish and seahorses as potential tankmates.

Gluttonous Nature.

Lionfish are gluttonous feeders and are known for eating way more than they require. Their stomachs can expand 30 times their normal volume creating room for their large appetites.

This great feeding frenzy can leave aquariums empty since these fish can empty tankmates digesting them one at a time.

As long as a creature can fit into their mouth they can be seen as potential prey. Keeping them should always be done with caution.

Risks Of Keeping Them Together.

While keeping Lionfish and seahorses together is highly unadvised some hobbyists are still willing to take a chance in hopes for a successful union.

These actions do come with immense risks that you should be aware of.

1. Your seahorses can be eaten by the lionfish in no time without any traces left behind. Seahorses are small and can easily fit in the mouth of a lionfish, making them ideal prey.

The gluttonous nature of a lionfish can be the end of your seahorses if kept together.

2. Lionfish have spines that can easily pierce through the fleshy layer of a seahorse leaving them immobile and susceptible to infection which can be fatal.

3. Most species of lionfish have venom delivered via an array of needle-like dorsal fins and any encounter can be potentially fatal. This venom can leave prey crippled leading to a painful death.

4. Their voracious appetites make them bad tankmates since they can easily outperform other tank occupants for resources.

Seahorses are not aggressive feeders they eat passively. If kept with lionfish, they will be outperformed receiving little to no nutrition.

5. These invasive fish when kept in captivity are known to prey on invertebrates which form clean-up crews.

Having these fish in your aquariums leaves your clean-up crew members at risk of falling prey to this predator.

6. They are threats to aquariums as well as in the wild and are known for drastically reducing marine populations. If kept, you should proceed with caution.

Alternative Ways Of Keeping Them?


Both seahorses and Lionfish are extremely aesthetic and unique making them great tank occupants in just about any aquarium.

Unfortunately, you can’t keep them together, however, you can keep them separately.

This will involve having two tanks that should cater to both species’ individual needs.

In this way, you get to keep both fish just so that they will be kept separately and safely.


If you are not interested in having two separate tanks rather look for other tank occupants that are similar to what you looking for.

For example, if you already have a seahorse aquarium and want to keep lionfish with them, you can opt for other suitable tankmates instead.

You can try a goby, royal gramma, or even certain types of clownfish that can be kept with seahorses.

Alternatively, if you already have a lionfish and want to keep seahorses, you can look for other replacements.

These include fish like angelfish, triggerfish, and puffers which are better fits for lionfish than seahorses.


Aquarium separators can be a possible solution for you to keep aggressive fish within the same tank as other peaceable fish.

It’s merely a plastic clear wall that you can easily mount onto the existing tank making clear separation of boundaries.

This can help keep both seahorses and lionfish in the same aquarium but without the possibility of danger.

The aquarium will remain the same with the water capacity and chemistry just the space will be limited and the filtration system will need to be strengthened.

Compatible Tankmates For Seahorses & LionFish

Tankmates For SeahorsesTankmates For Lionfish
1.  Goby 1. Angelfish
2. Cardinalfish2. Pufferfish
3. Dartfish 3. Blue Tang
4. Jawfish4. Maroon Clownfish
5. Dragonet5. Harlequin Tuskfish 
6. Pipefish6.  Clown Triggerfish
7. Molly Miller Blenny7. Groupers

Setting Up A Lionfish Aquarium.

Lionfish require very specific setups that cater to their individual needs. Let’s take a look at some of the requirements for a good lionfish aquarium.

1. Lionfish get pretty big and will therefore require enough space to thrive. A good starting point can be a 30-gallon tank that should be ideal for smaller species like the dwarfs.

For other larger species, it is recommended that they be housed in a minimum of 120 gallons.

2. Decor is also required, you can create your own aquascapes with rock and marine plants. But be sure to provide enough open space for free movement.

3. Lionfish require specific water parameters when kept in captivity. Recommended water conditions, 72-78° F, KH 8-12, pH 8.1-8.4, salinity 1.020-1.025

4. They require a proper filtration system with an addition of a protein skimmer. This will help create a strong system needed to filter through the water making sure water quality remains consistent.

5. Lionfish are carnivores that normally eat live food. When in captivity you can acclimate them to a diet of brine shrimp, squid, mysis shrimp, krill, and chopped fish. However, it’s better to buy a fish that’s already weaned to frozen food.

6. Maintenance is important to ensure water parameters. This should include daily filter, temperature, and chemical testing. Weekly quality tests and water changes (weekly or monthly) of about 10-25% of the total water volume as well as filter changes.

7. You can introduce suitable tankmates that can handle their aggressive nature but be sure to not overcrowd the tank.

8. Their aquarium must be placed away from direct sunlight in a safe low traffic area. This will help to maintain water temperature ensuring their survival.

Setting Up A Seahorse Aquarium.

Seahorses have very specific requirements for them to survive in captivity. They are more difficult to care for and are generally high maintenance.

1. They need mature water, free from ammonia and nitrite with low nitrate and phosphate levels.

2. As small as they are when kept in captivity they need ample water capacity to help dilute their heavy bioload.

This means larger tanks of appropriate dimensions to ensure stable water conditions.

3. They also need regular maintenance which includes water changes, water top-ups, and gravel siphoning.

4. They need an extra powered filtration system with the use of a protein skimmer to make sure water quality remains good.

5. They require moderate flow since they aren’t the best swimmers.

6. They must be away from direct sunlight and should have a cooler/heater to ensure specific water temperatures.

7. They require target feeding, to help reduce waste and detritus build-up which could be debilitating.

8. A good clean-up crew is also needed to cater to their messy tendencies and waste expulsions.

9. Many hitching posts are required for them to thrive since these areas are rest spots whereby they anchor themselves using their prehensile tail.

10. They need a species-specific tank due to their passive feeding habits and their sensitive nature.

When kept with tankmates they must be compatible with similar natures.

All these requirements help provide the optimal conditions needed for seahorses to thrive when kept in captivity.

Final Thoughts.

Lionfish and seahorses are both great marine life but must never be kept together. Seahorses have very special tankmate requirements and lionfish do not fit this criteria.

It’s best to keep them separate to avoid potential attacks and to keep seahorses from falling prey to these predators.

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